Reversible Thermochromic And Photochromic Ink Pens And Markers

ABSTRACT

Reversible thermochromic and photochromic ink compositions and markers, pens or writing instruments that use them are herein disclosed.

RELATED APPLICATIONS

This application claims benefit of priority to U.S. Provisional PatentApplication Ser. No. 61/584,398 filed Jan. 9, 2012 and U.S. ProvisionalPatent Application Ser. No. 61/732,120 filed Nov. 30, 2012, thedisclosures of which are incorporated herein by reference.

BACKGROUND

Ink is a liquid or paste that contains pigments or dyes and is used tocolor a surface to produce an image, text, or design. Ink is used fordrawing or writing with a pen, brush, or quill. Thicker inks, in pasteform, are used extensively in letterpress and lithographic printing.Conventional inks contain solvents, pigments, dyes, resins, lubricants,solubilizers, surfactants, particulate matter, fluorescers, and othermaterials. These materials control flow and thickness of the ink, andthe appearance of the ink when dry.

Ink colorants include pigments and dyes. Pigment inks are used morefrequently than dyes because they are more color-fast. Even so, pigmentsare often more expensive, less consistent in color, and have less of acolor range than dyes. Pigments are solid, opaque particles suspended inink to provide color. Pigment molecules typically link together incrystalline structures that are from 0.1-2 μm in size and usuallycomprise 5-30 percent of the ink volume. Qualities such as hue,saturation, and lightness vary depending on the source and type ofpigment.

Dye-based inks may have better color development than do pigment-basedinks, as they can produce more color density per unit of mass. However,because dyes are dissolved in the liquid phase, they have a tendency tosoak into paper, making the ink less efficient and potentially allowingthe ink to bleed at the edges of an image. To circumvent this problem,dye-based inks are made with solvents that dry rapidly or are used withquick-drying methods of printing, such as blowing hot air on the freshprint.

Chemicals that change color over a range of temperatures are known asthermochromic systems. Thermochromic chemicals can be manufactured tohave a color change that is reversible or irreversible. U.S. Pat. No.5,591,255, entitled “Thermochromic Ink Formulations, Nail Lacquer andMethods of Use”, issued Jan. 7, 1997 to Small et al., discloses methodsof producing thermochromic coating formulations without ingredientsknown to be harmful to thermochromic inks. The use of distilled water asa fountain solution for off-set printing using thermochromic ink is alsodisclosed.

Thermochromic systems use colorants that are either liquid crystals orleuco dyes. Liquid crystals are used less frequently than leuco dyesbecause they are very difficult to work with and require highlyspecialized printing and handling techniques. Thermochromic pigments area system of interacting parts. Leuco dyes act as colorants, while weakorganic acids act as color developers. Solvents or waxes variablyinteract with the leuco dyes according to the temperature of the system.As is known in the art, thermochromic systems are microencapsulated in aprotective coating to protect the contents from undesired effects fromthe environment. Each microcapsule is self-contained, having all of thecomponents of the entire system that are required for the color change.The components of the system interact with one another differently atdifferent temperatures. Generally, the system is ordered and coloredbelow a temperature corresponding to the full color point. The systembecomes increasingly unordered and starts to lose its color at atemperature corresponding to an activation temperature.

Below the activation temperature, the system is usually colored. Abovethe activation temperature the system is usually clear or lightlycolored. The activation temperature corresponds to a range oftemperatures at which the transition is taking place between the fullcolor point and the clearing point. Generally, the activationtemperature is the temperature at which the human eye can perceive thatthe system is starting to lose color, or alternatively, starting to gaincolor. Presently, thermochromic systems are designed to have activationtemperatures over a broad range, from about −20° C. to about 80° C. ormore. With heating, the system becomes increasingly unordered andcontinues to lose color until it reaches a level of disorder at atemperature corresponding to a clearing point. At the clearing point,the system lacks any recognizable color.

In this manner, thermochromic pigments change from a specific color toclear upon the application of thermal energy or heat in athermally-driven cycle exhibiting well-known hysteresis behavior.Thermochromic pigments come in a variety of colors. When applied to asubstrate, such as paper, the pigment exhibits the color of the dye atthe core of the microcapsules. In one example, when heat is appliedgenerally in the range of 30 to 32° C., the ink changes from the colorof the pigment to clear. When the substrate is allowed to return to atemperature under approximately 30° C., the ink returns to the originalcolor of the pigment.

U.S. Pat. No. 5,785,746, entitled “Preparation Method for Shear-ThinningWater-Based Ball-Point Pen Inks Compositions and Ball-Point PensEmploying the Same”, issued Jul. 28, 1998 to Kito et al., disclosesreversible thermochromic microcapsular pigment mixed in an inkcomposition. The microcapsules have concavities to moderate stressresulting from an external force during use in a ball-point pen.

U.S. Pat. No. 5,805,245, entitled “Multilayered Dispersed ThermochromicLiquid Crystal”, issued Sep. 8, 1998 to Davis, discloses a thermochromicsubstance, applied to inert films in stacked layers with a non-invasivebarrier between each thermochromic substance. The thermochromicsubstance in each layer responds in a different temperature range sothat as the temperature changes, each layer repeats a similar sequenceof colors. The substrate is a water-based acrylic copolymer formulationcoated or permeated with a black pigment. A transparent inert film ornon-invasive barrier serves as a protective coating for thethermochromic film and as a support for the next layer of thethermochromic substance.

Specific thermochromic coating formulations are known in the art. See,for example, U.S. Pat. Nos. 4,720,301, 5,219,625 5,558,700, 5,591,255,5,997,849, 6,139,779, 6,494,950 and 7,494,537, all of which areexpressly incorporated herein by reference. These thermochromic coatingsare known to use various components in their formulations, and aregenerally reversible in their color change. Thermochromic; pigments foruse in these coatings are commercially available in various colors, withvarious activation temperatures, clearing points and full color points.Thermochromic coatings may be printed by offset litho, dry offset,letterpress, gravure, flexo and screen processes, amongst others.

Ink pens have previously been developed that have thermochromic inkswhich can be activated by frictional heat into a colorless state. Thecolored form of the thermochromic ink cannot be regained withoutconsiderable difficulty. For example, reversing the thermochromictransition from colorless to color has previously required difficult andburdensome conditions, such as cooling the thermochromic ink to atemperature of about below the freezing point of water. In addition tobeing very difficult to regain or reverse the thermochromic transition,previous colored to colorless transitions do not allow for a color tocolor and/or black to color transitions.

SUMMARY

Presented herein are improved and novel reversible thermochromic andphotochromic ink compositions useful in pens and markers. Gel-ink andball-ink pens disclosed herein use thermochromic and photochromic inkcompositions, such as thermochromic ink that transitions from one colorto another color, and/or from color to colorless.

In one embodiment, the thermochromic ink compositions disclosed hereinare activated at about body temperature.

In one embodiment, the thermochromic ink compositions disclosed hereinare activated at about room temperature or higher than room temperature.

In one embodiment, the present disclosure relates to compositions forreversible thermochromic and photochromic inks useful in shear-thinningball-point pens, and a ball-point or gel-ink pen making use of the inkcomposition. The markers and pens using the ink compositions disclosedhave eliminated the difficulties involved in conventional ball-point penthermochromic and photochromic inks by providing thermochromic inkcompositions that allow for reversible thermochromic and photochromictransitions from color to color, black to color and novel color tocolorless transitions. The pens disclosed herein can give a smoothwriting touch.

A reversible thermochromic composition may contain, by way of example, areversible thermochromic pigment in an amount from 1% to 50% by weightof the ink. The reversible thermochromic pigment is susceptible to atemperature-modulated change of color between a first state and a secondstate along a thermally activated hysteresis loop. A non-thermochromicpigment is also provided. This may be, for example, a dye orphotochromic material. The non-thermochromic pigment is of a differentcolor from the reversible thermochromic pigment when the reversiblethermochromic pigment is in a colored state, such that thenon-thermochromic pigment and the reversible thermochromic pigmenttogether present a first color when the reversible thermochromic pigmentis in the first state and together present a second color when thereversible thermochromic pigment is in the second state. These pigmentsare mixed for substantially homogenous distribution in a vehicle as thebalance of the composition. This vehicle may be formulated to present anink for use in a ball point pen, a gel pen or a marker.

In one aspect, a thermochromic ink formulation shifts color, eitherreversibly or irreversibly, from one color to another color upon theapplication of heat to the ink or to the substrate on which the inkresides. The thermochromic ink formulation preferably includes one ormore thermochromic pigments in combination with a non-thermochromicpigment.

The ink may be formulated as a gel ink, a pen ink having less viscositythan the gel ink, or as a marker ink.

The ink may be formulated such that themochromic microcapsules are mixedwith a microencapsulated photochromic dye as the non-thermochromiccolorant.

DETAILED DESCRIPTION

A thermochromic ink formulation shifts from one color to another colorupon the application of heat, either to the ink or to the substrate onwhich the ink has been applied. The thermochromic ink formulationpreferably includes at least one thermochromic pigment in combinationwith a non-thermochromic colorant, such as a conventional pigment ordye. The non-thermochromic colorant may be any type of conventionalcolorant known to the art.

In some embodiments, the ink is formulated as a gel ink, substitutingthe colorants described herein for the colorants of a conventional gelink. In other embodiments, the ink is formulated as a pen ink,substituting the colorants described herein for the colorants of aconventional pen ink. In other embodiments, the formulation is used in amarker, substituting the colorants described herein for the colorants ofa conventional marker.

The thermochromic ink formulation includes at least two components, suchthat after creating an image on a substrate, e.g., paper, and upon theapplication of a certain amount of thermal energy, the image changesfrom one color to another color. The thermochromic ink formulation mayinclude, for example, thermochromic microcapsules and a conventionalpigment that differs in color from the developed color of thethermochromic pigment. The color of the thermochromic ink formulationmay be the dominant, or visible, color as the ink is applied to thesubstrate. However, upon the application of thermal energy to the inkimage, the thermochromic ink shifts from colored to clear, therebyallowing the non-dominant color of the non-thermochromic component tobecome visible.

In another example, a thermochromic pigment and a non-thermochromicpigment may be combined in relative proportions so that the combinedcolor pigments create a different color altogether when thethermochromic color is developed, and a second color when thethermochromic color is not developed. For example, the developed colorof the thermochromic pigment may be blue, while the color of thenon-thermochromic pigment may be yellow so that, when blended, theycreate a green color. Then, upon the application of thermal energy, thecolor of the thermochromic pigment goes to clear, thus allowing theyellow of the non-thermochromic pigment to dominate as the only visiblecolor. The result is that the color of the image goes from green toyellow when heated. The image returns to the “blended” green color whenthe image is allowed to cool past the color developing temperature. Theblending of a color-changing thermochromic ink with a static color inkprovides essentially limitless potential for the image.

Thermochromic pigments for use in formulations of the present disclosureare available commercially from a number of different manufacturers orsuppliers. Manufacturers of thermochromic inks include, but are notlimited to, Color Change Corporation (Streamwood, Illinois, US), LCRHallcrest (Glenview, Ill., US), Gem'innov (Gemenos, France), ISCALimited (Newport, Wales, UK), B&H Colour Change (London, England, UK),Thermographics Measurements Limited (Flintshire, UK), Fujian MecodeChemical Industry Company (Quanzhou, Fujian, China), and Matsui Color(Gardena, Calif., US). Distributors of thermochromic slurries include,but are not limited to, QCR Solutions Corporation (Port St. Lucie, Fla.,US), Woo Jeong Ind. Inc. (Seoul, South Korea), HW Sands Corp. (Jupiter,Fla., US), Devine Chemicals (Consett, England, UK), Chemical Plus(Bangkok, Thailand), and PMC Chemicals Limited (Altrincham, England,UK).

In a preferred embodiment, a thermochromic ink formulation includesthermochromic microcapsules in the thermochromic slurry that arespherical or substantially spherical in shape and exhibit a tightparticle size distribution in order to achieve a homogeneous dispersionin the thermochromic ink formulation. The thermochromic microcapsulesare preferably all small or substantially all small and are morepreferably all or substantially all under three micrometers in diameter.The thermochromic slurry preferably does not include flat orhemispherical microcapsules or microcapsules with surface concavities orother irregularities.

In a method of preparing a thermochromic ink formulation, athermochromic ink formulation is used as the pigment in a conventionalgel ink or a pen ink. The viscosity of the combination may be adjustedby adding compatible solvent to or removing solvent from the combinationto achieve the thermochromic ink formulation. The viscosity of thethermochromic ink formulation is preferably adjusted to a predeterminedvalue dependent upon the application for which the thermochromic inkformulation is to be used.

In some embodiments, the thermochromic ink formulation includes one ormore additives, which may include, but is not limited to, one or more ofa fluorescent additive, an optical brightener, and an infrared (IR)additive. In a non-limiting embodiment, the additive is used to providea covert or an over security benefit to a substrate to which thethermochromic ink formulation is applied.

A non-thermochromic colorant is preferably mixed with a thermochromicpigment in a ratio in the range of 1:1 to 3:1 by weight. Thenon-thermochromic colorant is more preferably mixed with thethermochromic pigment in a ratio in the range of 1.5:1 to 2.5:1 byweight. In some embodiments, the non-thermochromic colorant is mixedwith the thermochromic pigment in a ratio in the range of 1.9:1 to 2.1:1by weight. In one embodiment of the present invention, anon-thermochromic colorant is mixed with a thermochromic pigment in a2:1 ratio by weight.

In some embodiments, the ink is a gel fluorescent ink. In someembodiments, the color of the thermochromic pigment and the color of thenon-thermochromic colorant are contrasting or complementary and create ablend color in the thermochromic ink formulation below a criticaltemperature, although any combination of colors may be used within thespirit of the present invention.

In other embodiments, a thermochromic ink formulation includes more thanone thermochromic pigment such that at least two temperature-dependentcolor changes of the thermochromic ink formulation occur. Thethermochromic pigments preferably have different critical temperaturessuch that, in the case of a thermochromic ink formulation with twothermochromic pigments, at a first temperature below the criticaltemperatures of both thermochromic pigments, the formulation has a firstcolor, which is the sum of colors of the first thermochromic pigment,the second thermochromic pigment, and the non-thermochromic colorant. Ata temperature above the critical temperature of the first thermochromicpigment but below the critical temperature of the second thermochromicpigment, the formulation has a second color different from the firstcolor, which is the sum of colors of the second thermochromic pigmentand the non-thermochromic colorant. At a temperature above the criticaltemperatures of the first thermochromic pigment and the secondthermochromic pigment, the formulation has a third color different fromthe first and second colors, which is the color of the non-thermochromiccolorant. Any number of thermochromic pigments may be combined in thismanner.

In a non-limiting example, the thermochromic ink is blue, thenon-thermochromic pigment is fluorescent pink, the thermochromic pigmentis purple below a critical temperature, and the thermochromic inkformulation is pink above the critical temperature. In some embodiments,the process is reversible, with the thermochromic pigment returning to apurple color upon cooling below the critical temperature. In otherembodiments, the color change is irreversible. The reversibility of thecolor change depends on the hysteresis of the color change. Thereversibility of the color change is preferably selected based on thespecific application for the thermochromic ink.

In the case of a thermochromic ink formulation where the color changesare reversible, the thermochromic ink formulation may be used as avisual temperature range indicator, especially when multiplethermochromic pigments are used in the formulation to indicate multipletemperature thresholds. In the case of such a thermochromic inkformulation where the color changes are irreversible, the thermochromicink formulation may be used as a visual indicator of the maximumtemperature range to which the thermochromic ink formulation has beenexposed.

The critical temperature is also preferably selected based on thespecific application for the thermochromic ink. In some embodiments, thecritical temperature is below room temperature. In other embodiments,the critical temperature is above room temperature but below human bodytemperature such that the color change is triggered by human touch. Insome embodiments, the critical temperature is between 25 and 37° C. Insome embodiments, the critical temperature is about 31° C. In yet otherembodiments, the critical temperature is above human body temperaturesuch that another heat source is required to bring the ink to thecritical temperature.

In a non-limiting example, a thermochromic pen ink formulation or athermochromic gel ink formulation of the present invention is convertedto a thermochromic marker ink formulation of the present invention byadding about 10%; of water by volume to the thermochromic pen inkformulation or thermochromic gel ink formulation.

In some embodiments, a gel pen of the present invention includes athermochromic gel ink formulation of the present invention. In someembodiments, the gel pen includes an about 8-mm ball tip. In someembodiments, the ball tip is at least 8 mm in diameter. An 8-mm diameterball tip allows the passage of the thermochromic particles withoutdamaging the particles for some thermochromic gel ink formulations ofthe present invention.

In some embodiments, a marker of the present invention includes a markerink composition of the present invention. In some embodiments, themarker is a mechanical valve-type marker, also known as a paint marker,with a porous-type felt tip.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

Overview of Thermochromic Pigments

Reversible thermochromic and photochromic ink pens disclosed hereincontain thermochromic systems that are prepared by combining a colorforming molecule or molecules such as leuco dyes that are capable ofextended conjugation by proton gain or electron donation; a colordeveloper or developers that donate a proton or accept an electron; anda single solvent, or a blend of co-solvents. The solvent or blend ofco-solvents are chosen based on melting point and establish thethermochromic temperature range of the system. These formulations arethen microencapsulated within a polymeric shell.

These microcapsules encapsulate a thermochromic system mixed with asolvent. The thermochromic system has a material property of a thermallyconditional hysteresis window that presents a thermal separation.Thermochromic encapsulated dyes undergo a color change over a specifictemperature range. By way of example, a dye may change from a particularcolor at low temperature to colorless at a high temperature, such as redat 21° C. and colorless at above 33° C. The color change temperature iscontrollable, such that the color change can take place at differenttemperatures. In one example, the color change may occur at atemperature just below a person's external body temperature so that acolor change occurs in response to a human touch or may transition atabout room temperature. For example, the ideal temperature of colorchange may range from 12° C. to 15° C., 21° C. to 27° C., 23° C. to 27°C., 27° C. to 33° C. Custom thermochromic pigments and inks withspecified colors and transition temperature ranges may be formulated andproduced on commercial order from such companies as ChromaticTechnologies, Inc. of Colorado Springs, Colo.

Several types of ingredients are traditionally added to inkformulations. The combination of all the ingredients in an ink, otherthan the pigment, is called the vehicle. The vehicle carries the pigmentto the substrate and binds the pigment to the substrate. The correctcombination of vehicle ingredients will result in the wetting of an ink.This wetting means that the vehicle forms an absorbed film around thepigment particles. The main ingredient in an ink is the binder. This maybe a resin, lacquer or varnish or some other polymer. The bindercharacteristics vary depending on the type of printing that is beingdone and the desired final product. The second main ingredient is thecolorant itself, for example, as described above. The remainingingredients are added to enhance the color and printing characteristicsof the binder and the colorant. These remaining ingredients may includereducers (solvents), waxes, surfactant, thickeners, driers, and/or ITVinhibitors.

DEFINITIONS

Activation temperature—The temperature above which the ink has almostachieved its final clear or light color end point. The color starts tofade at approximately 4° C. below the activation temperature and will bein between colors within the activation temperature range.

Ball-point pen—As referred to herein, ball-point pens and gel-ink pensare interchangeable embodiments of pen means using reversiblethermochromic and photochromic ink compositions of the presentdisclosure. A ball-point pen may also be referred to as a marker. Aball-point pen may also be referred to as a writing instrument.

Clearing point—The temperature at which the color of a thermochromicsystem is diminished to a minimal amount and appears to lose no furthercolor density upon further heating.

Full color point—The temperature at which a thermochromic system hasachieved maximum color density upon cooling and appears to gain nofurther color density if cooled to a lower temperature.

A gel ink, as used herein, refers to a fluid composition including apigment suspended in a based gel. Gel inks typically have a higherviscosity than pen inks and can have a higher concentration of pigment.Gel inks are available in a wide variety of colors, including, but notlimited to, pastel colors, bright colors, metallic colors, glitterycolors, and opalescent colors. The pigments in a gel ink are generallynot in a dissolved state.

Gel-ink pen—As referred to herein, ball-point pens and gel-ink pens areinterchangeable embodiments of pen means using reversible thermochromicand photochromic ink compositions of the present disclosure. A gel-inkpen may also be referred to as a marker. A gel-ink pen may also bereferred to as a writing instrument.

Hysteresis—The difference in the temperature profile of a thermo chromicsystem when heated from the system when cooled.

Hysteresis window—The temperature difference in terms of degrees that athermochromic system is shifted as measured between the derivative plotof chroma of a spectrophotometer reading between the cooling curve andthe heating curve.

A marker, as used herein, refers to any writing instrument with a poroustip or felt tip made of a fibrous material for delivering ink. A pen, asused herein, refers to any non-marker, ink-based writing instrumentincluding, but not limited to, ball-point pens, roller-ball pens, andfountain pens.

A pen ink, as used herein, refers to a fluid or gel compositionincluding a pigment and a carrier or vehicle in which the pigment issuspended. In some embodiments, the vehicle is water. In otherembodiments, the solvent is a non-aqueous solvent, such as an organicsolvent such as alcohol. Photochromic ink—A mixture of dyes, solvents,and additives (encapsulated or non-encapsulated) that can undergoreversible color change in response to exposure to light of variouswavelengths.

Thermochromic system—A mixture of dyes, developers, solvents, andadditives (encapsulated or non-encapsulated) that can undergo reversiblecolor change in response to temperature changes.

Thermochromic ink—An ink that contains a pigment formed of a mixture ofdyes, developers, solvents, and additives that are encapsulated and canundergo reversible color change in response to temperature changes. Thecolor change is based upon the action of micrpoencapsulated leuco dyesand developers, which are referred to herein as thermochromic pigments.Thermochromic pigments may be sold as dry powders or in water-basedslurries of encapsulated dye.

Leuco dye—A leuco dye is a dye whose molecules can acquire two forms,one of which is colorless.

Thermochromic Inks

Thermochromic inks useful in ball-point pens and gel-ink pens containmicrocapsules, which encapsulate a thermochromic system mixed with asolvent. The thermochromic system has a material property of a thermallyconditional hysteresis window that presents a thermal separation. Theseinks may be improved according to the instrumentalities described hereinby using a co-solvent that is combined with the thermochromic system andselected from the group consisting of derivatives of mysristic acid,derivatives of behenyl acid, derivatives of palmytic acid andcombinations thereof. This material may be provided in an effectiveamount to reduce the thermal separation in the overall ink to a levelless than eighty percent of separation that would otherwise occur if thematerial were not added. This effective amount may range, for examplefrom the 12% to 15% by weight of the composition.

The thermochromic system may contain, for example, at least onechromatic organic compound and co-solvents.

One example of a thermochromic system includes a leuco dye having alactone ring structure and a phenolic developer. Within the encapsulatedthermochromic systems, complexes form between the dye and the weak aciddeveloper that allow the lactone ring structure of the leuco dye to beopened. The nature of the complex is such that the hydroxyl groups ofthe phenolic developer interact with the open lactone ring structureforming a supra-molecular structure that orders the dyes and developerssuch that a color is formed. Color forms from this supra-molecularstructure because the dye molecule in the ring open structure iscationic in nature and the molecule has extended conjugation allowingabsorption in the visible spectrum thus producing a colored species. Thecolor that is perceived by the eye is what visible light is not absorbedby the complex. The nature of the dye/developer complex depends on themolar ratio of dye and developer. The stability of the colored complexis determined by the affinity of the solvent for itself, the developeror the dye/developer complex. In a solid state, below the full colorpoint, the dye/developer complex is stable. In the molten state, thesolvent destabilizes the dye/developer complex and the equilibrium ismore favorably shifted towards a developer/solvent complex. This happensat temperatures above the full color point because the dye/developercomplex is disrupted and the extended conjugation of the π cloudelectrons that allow for the absorption of visible light are destroyed.

The melting and crystallization profile of the solvent system determinesthe nature of the thermochromic system. The full color point of thesystem occurs when the maximum amount of dye is developed. In acrystallized solvent state, the dye/developer complex is favored wherethe dye and developer exist in a unique crystallized structure, oftenintercalating with one another to create an extended conjugated asystem. In the molten state, the solvent(s), in excess, have enoughkinetic energy to disrupt the stability of the dye/developer complex,and the thermochromic system becomes decolorized.

The addition of a co-solvent with a significantly higher melting pointthan the other dramatically changes the melting properties of both thesolvents. By mixing two solvents that have certain properties, a blendcan be achieved that possesses a eutectic melting point. The meltingpoint of a eutectic blend is lower than the melting point of either ofthe co-solvents alone and the melting point is sharper, occurring over asmaller range of temperatures. The degree of the destabilization of thedye/developer complex can be determined by the choice of solvents. Bycreating unique eutectic blends, both the clearing point and the fullcolor point can be altered simultaneously. The degree of hysteresis isthen shifted in both directions simultaneously as the sharpness of themelting point is increased.

Temperature changes in thermochromic systems are associated with colorchanges. If this change is plotted on a graph having axes of temperatureand color, the curves do not align and are offset between the heatingcycle and the cooling cycle. The entire color versus temperature curvehas the form of a loop. Such a result shows that the color of athermochromic system does not depend only on temperature, but also onthe thermal history, i.e. whether the particular color was reachedduring heating or during cooling. This phenomenon is generally referredto as a hysteresis cycle and specifically referred to herein as colorhysteresis or the hysteresis window. Decreasing the width of thishysteresis window to approximately zero would allow for a single valuefor the full color point and a single value for the clearing point. Thiswould allow for a reliable color transition to be observed regardless ofwhether the system is being heated or cooled. Nonetheless, the conceptdecreasing separation across the hysteresis window is elusive inpractice. Thus, it is an object of the present disclosure to providethermochromic systems with a reduced hysteresis window achieved byshifting both the full color point and the clearing point such as inmemory inks, for example.

It is also an object of this disclosure to provide formulations ofextended hysteresis windows in ink formulations.

Leuco Dyes

Leuco dyes most commonly used as color formers in thermochromic systemsof the present disclosure include, but are not limited to, generally;spirolactones, fluorans, spiropyrans, and fulgides; and morespecifically; diphenylmethane phthalide derivatives,phenylindolylphthalide derivatives, indolylphthalide derivatives,diphenylmethane azaphthalide derivatives, phenylindolylazaphthalidederivatives, fluoran derivatives, styrynoquinoline derivatives, anddiaza-rhodamine lactone derivatives which can include:3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide;3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl) phthalide;3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalide;3,3-bis(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide;3-[2-ethoxy-4-(N-ethylanilino)phenyl]-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide;3,6-dimethoxyfluoran; 3,6-di-n-butoxyfluoran;2-methyl-6-(N-ethyl-N-p-tolylamino)fluoran;3-chloro-6-cyclohexylaminofluoran; 2-methyl-6-cyclohexylaminofluoran;2-(2-chloroanilino)-6-di-n-butylamino fluoran;2-(3-trifluoromethylanilino)-6-diethylaminofluoran;2-(N-methylanilino)-6-(N-ethyl-N-p-tolylamino) fluoran,1,3-dimethyl-6-diethylaminofluoran; 2-chloro-3-methyl-6-diethylaminofluoran; 2-anilino-3-methyl-6-diethylaminofluoran;2-anilino-3-methyl-6-di-n-butylamino fluoran;2-xylidino-3-methyl-6-diethylaminofluoran;1,2-benzo-6-diethylaminofluoran;1,2-benzo-6-(N-ethyl-N-isobutylamino)fluoran,1,2-benzo-6-(N-ethyl-N-isoamylamino)fluoran;2-(3-methoxy-4-dodecoxystyryl)quinoline;spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one;2-(diethylamino)-8-(diethylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one;2-(di-n-butylamino)-8-(di-n-butylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one;2-(di-n-butylamino)-8-(diethylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one;2-(di-n-butylamino)-8(N-ethyl-N-isoamylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one;and 2-(di-n-butylamino)-8-(di-n-butylamino)-4-phenyl and trisubstitutedpyridines.

Developers

Weak acids that can be used as color developers act as proton donors,changing the dye molecule between its leuco form and its protonatedcolored form; stronger acids make the change irreversible. Examples ofdevelopers used in the present disclosure include but are not limitedto: bisphenol A; bisphenol F; tetrabromobisphenol A;1′-methylenedi-2-naphthol; 1,1,1-tris(4-hydroxyphenyl)ethane;1,1-bis(3-cyclohexyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene; 1-naphthol; 2-naphthol;2,2 bis(2-hydroxy-5-biphenylyl)propane;2,2-bis(3-cyclohexyl-4-hydroxy)propane;2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(4-hydroxyphenyl)propane; 2,3,4-trihydroxydiphenylmethane;4,4′-(1,3-Dimethylbutylidene)diphenol; 4,4′-(2-Ethylidene)diphenol;4,4′-(2-hydroxybenzylidene)bis(2,3,6-trimethylphenol); 4,4′-biphenol;4,4′-dihydroxydiphenyl ether; 4,4′-dihydroxydiphenylmethane;4,4′-methylidenebis(2-methylphenol); 4-(1,1,3,3-tetramethylbutyl)phenol;4-phenylphenol; 4-tert-butylphenol; 9,9-bis(4-hydroxyphenyl)fluorine;4,4′-(ethane-1,1-diyl)diphenol;alpha,alpha′-bis(4-hydroxyphenyl)-1,4-diisopropylbenzene;alpha,alpha,alpha′-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene;benzyl 4-hydroxybenzoate; bis(4-hydroxyphenyl)sulfide;bis(4-hydroxyphenyl)sulfone; propyl 4-hydroxyhenzoate; methyl4-hydroxyhbenzoate; resorcinol; 4-tert-butyl-catechol;4-tert-butyl-benzoic acid; 1,1′-methylenedi-2-naphthol1,1,1-tris(4-hydroxyphenyl)ethane;1,1-bis(3-cyclohexyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene; 1-naphthol 2,2′-biphenol;2,2-bis(2-hydroxy-5-biphenylyl)propane;2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane;2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(4-hydroxyphenyl)propane; 2,3,4-trihydroxydiphenylmethane;2-naphthol; 4,4′-(1,3-dimethylbutylidene)diphenol;4,4′-(2-ethylhexylidene)diphenol4,4′-(2-hydroxybenzylidene)bis(2,3,6-trimethylphenol); 4,4′-biphenol;4,4′-dihydroxydiphenyl ether; 4,4′-dihydroxydiphenylmethane;4,4′-ethylidenebisphenol; 4,4′-methylenebis(2-methylphenol);4-(1,1,3,3-tetramethylbutyl)phenol; 4-phenylphenol; 4-tert-butylphenol;9,9-bis(4-hydroxyphenyl)fluorine;alpha,alpha′-bis(4-hydroxyphenyl)-1,4-diisopropylbenzene;α,α,α-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene; benzyl4-hydroxybenzoate; bis(4-hydroxyphenyl) sulfidem; bis(4-hydroxyphenyl)sulfone methyl 4-hydroxybenzoate; resorcinol; tetrabromobisphenol A;3,5-di-tertbutyl-salicylic acid; zinc 3,5-di-tertbutylsalicylate;3-phenyl-salicylic acid; 5-tertbutyl-salicylic acid; 5-n-octyl-salicylicacid; 2,2′-biphenol; 4,4′-di-tertbutyl-2,2′-biphenol;4,4′-di-n-alkyl-2,2′-biphenol; and 4,4′-di-halo-2,2′-biphenol, whereinthe halo is chloro, fluoro, bromo, or iodo.

Solvents

The best solvents to use within the thermochromic system are those thathave low reactivity, have a relatively large molecular weight (i.e. over100), and which are relatively non-polar. Very low molecular weightaldehydes, ketones, diols and aromatic compounds should not be used assolvents within the thermochromic system.

Thermochromic inks disclosed herein use a co-solvent that is combinedwith the thermochromic system and selected from the group consisting ofderivatives of mysristic acid, derivatives of behenyl acid, derivativesof palmytic acid and combinations thereof. This material may be providedin an effective amount to reduce the thermal separation in the overallink to a level less than eighty percent of separation that wouldotherwise occur if the material were not added. This effective amountmay range, for example from the 12% to 15% by weight of the composition.

The addition of a co-solvent with a significantly higher melting pointthan the other dramatically changes the melting properties of both thesolvents. By mixing two solvents that have certain properties, a blendcan be achieved that possesses a eutectic melting point. The meltingpoint of a eutectic blend is lower than the melting point of either ofthe co-solvents alone and the melting point is sharper, occurring over asmaller range of temperatures. The degree of the destabilization of thedye/developer complex can be determined by the choice of solvents. Bycreating unique eutectic blends, both the clearing point and the fullcolor point can be altered simultaneously. The degree of hysteresis isthen shifted in both directions simultaneously as the sharpness of themelting point is increased. Copending application Ser. No. 13/363,070filed Jan. 31, 2012 discloses thermochromic systems with controlledhysteresis, and is hereby incorporated by reference to the same extentas though fully replicated herein. According to the instrumentalitiesdescribed therein, the microencapsulate pigments may be formulated tohave color transition temperatures across a hysteresis window of lessthan five degrees centigrade or more than 60 or 80 degrees centigrade.

Properties of at least one of the co-solvents used in the presentdisclosure include having a long fatty tail of between 12 and 24 carbonsand possessing a melting point that is about 70° C. to about 200° C.greater than the co-solvent partner. The co-solvents are preferably alsocompletely miscible at any ratio.

Solvents and/or co-solvents used in thermochromic generally may include,but are not limited to, sulfides, ethers, ketones, esters, alcohols, andacid amides. These solvents can be used alone or in mixtures of 2 ormore. Examples of the sulfides include: di-n-octyl sulfide; di-n-nonylsulfide; di-n-decyl sulfide; di-n-dodecyl sulfide; di-n-tetradecylsulfide; di-n-hexadecyl sulfide; di-n-octadecyl sulfide; octyl dodecylsulfide; diphenyl sulfide; dibenzyl sulfide; ditolyl sulfide;diethylphenyl sulfide; dinaphthyl sulfide; 4,4′-dichlorodiphenylsulfide; and 2,4,5,4′tetrachlorodiphenyl sulfide. Examples of the ethersinclude: aliphatic ethers having 10 or more carbon atoms, such asdipentyl ether, dihexyl ether, diheptyl ether, dioctyl ether, dinonylether, didecyl ether, diundecyl ether, didodecyl ether, ditridecylether, ditetradecyl ether, dipentadecyl ether, dihexadecyl ether,dioctadecyl ether, decanediol dimethyl ether, undecanediol dimethylether, dodecanediol dimethyl ether, tridecanediol dimethyl ether,decanediol diethyl ether, and undecanediol diethyl ether; alicyclicethers such as s-trioxane; and aromatic ethers such as phenylether,benzyl phenyl ether, dibenzyl ether, di-p-tolyl ether,1-methoxynaphthalene, and 3,4,5trimethoxytoluene.

Examples of ketone solvents include: aliphatic ketones having 10 or morecarbon atoms, such as 2-decanone, 3-decanone, 4-decanone, 2-undecanone,3-undecanone, 4-undecanone, 5-undecanone, 6-undecanone, 2-dodecanone,3-dodecanone, 4-dodecanone, 5-dodecanone, 2-tridecanone, 3-tridecanone,2-tetradecanone, 2-pentadecanone, 8-pentadecanone, 2-hexadecanone,3-hexadecanone, 9-heptadecanone, 2-pentadecanone, 2-octadecanone,2-nonadecanone, 10-nonadecanone, 2-eicosanone, 11-eicosanone,2-heneicosanone, 2-docosanone, laurone, and stearone; aryl alkyl ketoneshaving 12 to 24 carbon atoms, such as n-octadecanophenone,n-heptadecanophenone, n-hexadecanophenone, n-pentadecanophenone,n-tetradecanophenone, 4-n-dodecaacetophenone, n-tridecanophenone,4-n-undecanoacetophenone, n-laurophenone, 4-n-decanoacetophenone,n-undecanophenone, 4-n-nonylacetophenone, n-decanophenone,4-n-octylacetophenone, n-nonanophenone, 4-n-heptylacetophenone,n-octanophenone, 4-n-hexylacetophenone, 4-n-cyclohexylacetophenone,4-tert-butylpropiophenone, n-heptaphenone, 4-n-pentylacetophenone,cyclohexyl phenyl ketone, benzyl n-butyl ketone, 4-n-butylacetophenone,n-hexanophenone, 4-isobutylacetophenone, 1-acetonaphthone,2-acetonaphthone, and cyclopentyl phenyl ketone; aryl aryl ketones suchas benzophenone, benzyl phenyl ketone, and dibenzyl ketone; andalicyclic ketones such as cyclooctanone, cyclododecanone,cyclopentadecanone, and 4-tert-butylcyclohexanone, ethyl caprylate,octyl caprylate, stearyl caprylate, myristyl caprate, stearyl caprate,docosyl caprate, 2-ethylhexyl laurate, n-decyl laurate, 3-methylbutylmyristate, cetyl myristate, isopropyl palmitate, neopentyl palmitate,nonyl palmitate, cyclohexyl palmitate, n-butyl stearate, 2-methylbutylstearate, stearyl behenate 3,5,5-trimethylhexyl stearate, n-undecylstearate, pentadecyl stearate, stearyl stearate, cyclohexylmethylstearate, isopropyl behenate, hexyl behenate, lauryl behenate, behenylbehenate, cetyl benzoate, stearyl p-tert-butylbenzoate, dimyristylphthalate, distearyl phthalate, dimyristyl oxalate, dicetyl oxalate,dicetyl malonate, dilauryl succinate, dilauryl glutarate, diundecyladipate, dilauryl azelate, di-n-nonyl sebacate,1,18-dineopentyloctadecylmethylenedicarboxylate, ethylene glycoldimyristate, propylene glycol dilaurate, propylene glycol distearate,hexylene glycol dipalmitate, 1,5-pentanediol dimyristate,1,2,6-hexanetriol trimyristate, 1,4-cyclohexanediol didecanoate,1,4-cyclohexanedimethanol dimyristate, xylene glycol dicaprate, andxylene glycol distearate.

Ester solvents can be selected from esters of a saturated fatty acidwith a branched aliphatic alcohol, esters of an unsaturated fatty acidor a saturated fatty acid having one or more branches or substituentswith an aliphatic alcohol having one or more branches or 16 or morecarbon atoms, cetyl butyrate, stearyl butyrate, and behenyl butyrateincluding 2-ethylhexyl butyrate, 2-ethylhexyl behenate, 2-ethylhexylmyristate, 2-ethylhexyl caprate, 3,5,5-trimethylhexyl laurate,3,5,5-trimethylhexyl palmitate, 3,5,5-trimethylhexyl stearate,2-methylbutyl caproate, 2-methylbutyl caprylate, 2-methylbutyl caprate,1-ethylpropyl palmitate, 1-ethylpropyl stearate, I-ethylpropyl behenate,1-ethylhexyl laurate, 1-ethylhexyl myristate, 1-ethythexyl palmitate,2-methylpentyl caproate, 2-methylpentyl caprylate, 2-methylpentylcaprate, 2-methylpentyl laurate, 2-methylbutyl stearate, 2-methylbutylstearate, 3-methylbutyl stearate, 2-methylheptyl stearate, 2-methylbutylbehenate, 3-methylbutyl behenate, 1-methylheptyl stearate,1-methylheptyl behenate, 1-ethylpentyl caproate, 1-ethylpentylpalmitate, 1-methylpropyl stearate, 1-methyloctyl stearate,1-methylhexyl stearate, 1,1dimethylpropyl laurate, 1-methylpentylcaprate, 2-methylhexyl palmitate, 2-methylhexyl stearate, 2-methylhexylbehenate, 3,7-dimethyloctyl laurate, 3,7-dimethyloctyl myristate,3,7-dimethyloctyl palmitate, 3,7-dimethyloctyl stearate,3,7-dimethyloctyl behenate, stearyl oleate, behenyl oleate, stearyllinoleate, behenyl linoleate, 3,7-dimethyloctyl erucate, stearylerucate, isostearyl erucate, cetyl isostearate, stearyl isostearate,2-methylpentyl 12-hydroxystearate, 2-ethylhexyl 18-bromostearate,isostearyl 2-ketomyristate, 2-ethylhexyl-2-fluoromyristate, cetylbutyrate, stearyl butyrate, and behenyl butyrate.

Examples of the alcohol solvents include monohydric aliphatic saturatedalcohols such as decyl alcohol, undecyl alcohol, dodecyl alcohol,tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, hexadecylalcohol, heptadecyl alcohol, octadecyl alcohol, eicosyl alcohol, behenylalcohol and docosyl alcohol; aliphatic unsaturated alcohols such asallyl alcohol and oleyl alcohol, alicyclic alcohols such ascyclopentanol, cyclohexanol, cyclooctanol, cyclododecanol, and4-tert-butylcyclohexanol; aromatic alcohols such as 4-methylbenzylalcohol and benzhydrol; and polyhydric alcohols such as polyethyleneglycol. Examples of the acid amides include acetamide, propionamide,butyramide, capronamide, caprylamide, capric amide, lauramide,myristamide, palmitamide, stearamide, behenamide, oleamide, erucamide,benzamide, capronanilide, caprylanilide, capric anilide, lauranilide,myristanilide, palmitanilide, stearanilide, behenanilide, oleanilide,erucanilide, N-methylcapronamide, N-methylcaprylamide, N-methyl (capricamide), N-methyllauramide, N-methylmyristamide, N-methylpalmitamide,N-methylstearamide, N-methylbehenamide, N-methyloleamide,N-methylerucamide, N-ethyllauramide, N-ethylmyristamide,N-ethylpalmitamide, N-ethylstearamide, N-ethyloleamide,N-butyllauramide, N-butylmyristamide, N-butylpalmitamide,N-butylstearamide, N-butyloleamide, N-octyllauramide,N-octylmyristamide, N-octylpalmitamide, N-octylstearamide,N-octyloleamide, N-dodecyllauramide, N-dodecylmyristamide,N-dodecylpalmitamide, N-dodecylstearamide, N-dodecyloleamide,dilauroylamine, dimyristoylamine, dipalmitoylamine, distearoylamine,dioleoylamine, trilauroylamine, trimyristoylamine, tripalmitoylamine,tristearoylamine, trioleoylamine, succinamide, adipamide, glutaramide,malonamide, azelamide, maleamide, N-methylsuccinamide, N-methyladipamide, N-methylglutaramide, N-methylmalonamide, N-methylazelamide,N-ethylsuccinamide, N-ethyladipamide, N-ethylglutaramide,N-ethylmalonamide, N-ethylazelamide, N-butylsuccinamide,N-butyladipamide, N-butylglutaramide, N-butylmalonamide,N-octyladipamide, and N-dodecyladipamide.

Among these solvents, it has been discovered that certain solvents havethe effect of reducing the hysteresis window. The solvent may bematerial combined with the thermochromic system, for example, to reducethermal separation across the hysteresis window to a level demonstrating80%, 70%, 50%, 40%, 30% or less of the thermal separation that wouldexist if the co-solvent were not present. The co-solvent is selectedfrom the group consisting of derivatives of mysristic acid, derivativesof behenyl acid, derivatives of palmytic acid and combinations thereof.Generally, these materials include myristates, palmitates, behenates,together with myristyl, stearyl, and behenyl materials and certainalcohols. In one aspect, these materials are preferably solvents andco-solvents from the group including isopropyl myristate, isopropylpalmitate, methyl palmitate, methyl stearate, myristyl myristate, cetylalcohol, stearyl alcohol, behenyl alcohol, stearyl behenate, andstearamide. These co-solvents are added to the encapsulatedthermochromic system in an amount that, for example, ranges from 9% to18% by weight of the thermochromic system as encapsulated, i.e.,excluding the weight of the capsule. This range is more preferably fromabout 12% to about 15% by weight.

Light Stabilizers

Thermochromic inks containing leuco dyes are available for all major inktypes such as water-based, ultraviolet cured and epoxy. The propertiesof these inks differ from process inks. For example, most thermochromicinks contain the thermochromic systems as microcapsules, which are notinert and insoluble as are ordinary process pigments. The size of themicrocapsules containing the thermochromic systems ranges typicallybetween 3-5 μm which is more than 10-times larger than regular pigmentparticles found in most inks. The post-print functionality ofthermochromic inks can be adversely affected by ultraviolet light,temperatures in excess of 140° C. and aggressive solvents. The lifetimeof these inks is sometimes very limited because of the degradationcaused by exposure to ultraviolet light from sunlight.

In other instances, additives used to fortify the encapsulatedthermochromic systems by imparting a resistance to degradation byultraviolet light by have a dual functionality of also reducing thewidth of separation over the hysteresis window. Light stabilizers areadditives which prevent degradation of a product due to exposure toultraviolet radiation. Examples of light stabilizers used inthermochromic systems of the present disclosure and which may alsoinfluence the hysteresis window include but are not limited to:avobenzone, bisdisulizole disodium, diethylaminohydroxybenzoyl hexylbenzoate, Ecamsule, methyl anthranilate, 4-aminobenzoic acid, Cinoxate,ethylhexyl triazone, homosalate, 4-methylbenzylidene camphor, octylmethoxycinnamate, octyl salicylate, Padimate 0, phenylbenzimidazolesulfonic acid, polysilicone-15, trolamine salicylate, bemotrizinol,benzophenones 1-12, dioxybenzone, drometrizole trisiloxane,iscotrizinol, octocrylene, oxybenzone, sulisobenzone, bisoctrizole,titanium dioxide and zinc oxide.

Careful preparation of encapsulated reversible thermochromic materialenhances coating stability in the presence of low molecular weight polarsolvents that are known to adversely affect thermochromic behavior. Oneskilled in the art of microencapsulation can utilize well-knownprocesses to enhance the stability of the microcapsule. For example, itis understood that increasing the cross linking density will reduce thepermeability of the capsule wall, and so also reduces the deleteriouseffects of low molecular weight solvents. It is also commonly understoodthat, under certain conditions, weak acids with a pKa greater than about2 may catalyze microcapsule wall polymerization and increase theresulting cross linking density. It is presently the case that usingformic acid as a catalyst enhances solvent stability of bluethermochromic microcapsules in the presence of low molecular weightketones, diols, and aldehydes at room temperature. Further, it is wellunderstood that increasing the diameter of the thermochromicmicrocapsule can result in enhanced solvent stability.

The selection of material for use as the non-polar solvent for thethermochromic dye and color developer that is encapsulated within thethermochromic pigment determines the temperature at which color changeis observed. For example, changing the solvent from a single componentto a two component solvent system can shift the temperature at whichfull color is perceived almost 7° C. from just under 19° C. to 12° C.The present disclosure shows how to apply this knowledge in preparingresin-based vehicle coatings for use in can and coil coatings with fullcolor temperatures, i.e., the temperature at which maximum colorintensity is observed, as low as −5° C. and as high as 65° C. No adverseeffects on the physical properties of the resulting coating wereobserved as the full color temperature was changed over the above rangeby the use of different straight chain alkyl esters, alcohols, ketonesor amides.

Thermochromic materials including encapsulated thermochromic systemswith a variety of color properties may be purchased on commercial orderfrom such companies as Chromatic Technologies, Inc., of ColoradoSprings, Colo.

Control over observed color intensity is demonstrated in several ways,generally by providing increased amounts of pigment. For a typicalcoating, material thickness ranges from 1 mg/in2 to 6 mg/in2. Veryintense color is observed for coatings with thickness greater than about3 mg/in2. Increasing thermochromic pigment solids can also result in amore intense observed color even when coating thickness is decreased.However, dried film properties such as flexibility and toughness may becompromised if too much thermochromic pigment is incorporated. Theoptimal range of thermochromic pigment solids is within 5 to 40′ byweight of the coating.

Vehicle

Physical properties of the finished coating can be significantlyaffected by the selection of resin to be used. When no resin is used informulating a reversible thermochromic coating, a matte finish isachieved that is able to be formed into can ends, tabs, caps and/orother closures. While this result may be desired, the inclusion of a lowviscosity, relatively low molecular weight resin, monomer, oligomer,polymer, or combination thereof, can enhance gloss and affect otherphysical film properties such as hardness, flexibility and chemicalresistance. The resin is designed to supplement the total solidsdeposited on the substrate, thus impacting the physical properties ofthe dried film. Any resin material, monomer, oligomer, polymer, orcombination thereof that can be polymerized into the commerciallyavailable can and coil coating material is suitable for inclusion in theformulation of the current reversible thermochromic can and coilcoating. Acceptable classes of resins include, but are not limited topolyester, urethane, acrylic acid and acrylate, or other types of resinsystems with suitably high solids content.

Encapsulation Process

Nearly all thermochromic systems require encapsulation for protection.As is known in the art, the most common process for encapsulation isinterfacial polymerization. During interfacial polymerization theinternal phase (material inside the capsule), external phase (wallmaterial of the capsule) and water are combined through high-speedmixing. By controlling all the temperature, pH1, concentrations, andmixing speed precisely, the external phase will surround the internalphase droplet while crosslinking with itself. Usually the capsules arebetween 3-5 μm or smaller. Such small sizes of capsules are referred toas microcapsules and the thermochromic system within the microcapsulesare microencapsulated. Microencapsulation allows thermochromic systemsto be used in wide range of materials and products. The size of themicrocapsules requires some adjustments to suit particular printing andmanufacturing processes.

The size distribution of microcapsules can range from as much as 0.2 μmto 100 μm. Further example techniques of physical microencapsulationinclude but are not limited to pan coating, air suspension coating,centrifugal extrusion, vibration nozzle, and spray drying. Examples ofchemical microencapsulation techniques include but are not limited tointerfacial polymerization, in-situ polymerization, and matrixpolymerization. Example polymers used in the preferred chemicalmicroencapsulation include but are not limited to polyester,polyurethane, polyureas, urea-formaldehyde, epoxy,melamnine-formaldehyde, polyethylene, polyisocyanates, polystyrene,polyamides, and polysilanes.

The capsule isolates the thermochromic system from the environment, butthe barrier that the capsule provides is itself soluble to certainsolvents. Therefore, the microcapsule constituents interact with theenvironment to some extent. The solubility parameter describes how mucha material will swell in the presence of different solvents. Thisswelling will directly impact the characteristics of the reactionpotential within the capsule, as well as potentially making the capsulemore permeable, both of which will likely adversely affect thethermochromic system. Solvents in which the microcapsules are exposed toare chosen so as not to destroy, or affect, the thermochromic systemwithin.

The capsule is hard, thermally stable and relatively impermeable. Theinfiltration of compounds through the capsule are stopped or slowed tothe point that the characteristics of the dye are not affected. Thepollution of the thermochromic system within the capsule by solventsfrom the environment affects the shelf life of the thermochromic system.Therefore, the formulation of the applied thermochromic system, as anink for example, should be carefully considered.

In an embodiment of the present disclosure, capsules are made from ureaformaldehyde. One technique used to produce the encapsulatedthermochromic systems is to combine water, dye, oil, and ureaformaldehyde and mix to create a very fine emulsification. Because ofthe properties of the compounds, the oil and dye end up on the inside ofthe capsule and the water ends up on the outside, with the ureaformaldehyde making up the capsule itself. The capsule can then bethermo-set, similar to other resins, such as formica. The thermo-setsubstance is very hard and will not break down, even at temperatureshigher than the encapsulated thermochromic system is designed to beexposed to. The urea formaldehyde capsule is almost entirely insolublein most solvents, but it is permeable to certain solvents that mightdestroy the ability of the thermochromic system to color and decolorizethroughout a temperature range.

The extent to which capsules will react with their environment isinfluenced by the pH of the surrounding medium, the permeability of thecapsule, the polarity and reactivity of compounds in the medium, and thesolubility of the capsule. Preferred media used in formulatingencapsulated thermochromic system are engineered to reduce thereactivity between that medium and the capsules to a low enough levelthat the reactivity will not influence the characteristics of the dyefor an extended period of time.

Highly polar solvent molecules, with the exception of water, ofteninteract more with the leuco dye than with the capsule shell and othernon-polar molecules of the thermochromic system. Therefore, polarsolvents that are able to cross the capsule barrier should, in general,be eliminated from the medium within which the encapsulatedthermochromic system is formulated.

Aqueous media that the encapsulated thermochromic systems are placedwithin should have a narrow pH range from about 6.5 to about 7.5. Whenan encapsulated thermochromic system is added to a formulation that hasa pH outside this range, often the thermochromic properties of thesystem are destroyed. This is an irreversible effect.

One aspect of the present disclosure is for a method of improving theformulations of the thermochromic system by removing any aldehydes,ketones, and diols and replacing them with solvents which do notadversely affect the thermochromic system. Solvents having a largemolecular weight (i.e. greater than 100) generally are compatible withthe thermochromic systems. The acid content of the system is preferablyadjusted to an acid number below 20 or preferably adjusted to beneutral, about 6.5-7.5. Implementing these solvent parameters for use inthe thermochromic system will preserve the reversible coloration abilityof the leuco dyes.

Formulations for thermochromic systems are engineered with all theconsiderations previously mentioned. The examples below describe athermochromic system with excellent color density, low residual color,narrow temperature ranges between full color and clearing point, and anarrow hysteresis window. The full color point and the clearing pointare determined by visual inspection of the thermochromic system at arange of temperatures. The difference in temperature between the maximaof color change during the cooling cycle and the heating cycle is usedto calculate hysteresis.

Adjusting the Acid Content

Water-based inks are pH adjusted prior to addition of thermochromicpigment. As mentioned above, the pH should be neutral unless observationindicates that a different pH is required. To achieve the correct pH,one uses a good proton donor or acceptor, depending on whether the pH isto be adjusted up or down. To lower the pH, sulfuric acid is used, toraise it, the best proton acceptor so far is KOH. These two chemicalsare very effective and do not seem to impart undesirable characteristicsto the medium. The most effective pH is about 7.0, however, sometolerance has been noted between 6.0 and 8.0. A pH below 6.0 and above8.0 has almost always immediately destroyed the pigment.

The acid value is defined as the number of milligrams of a 0.1 N KOHsolution required to neutralize the alkali reactive groups in 1 gram ofmaterial under the conditions of ASTM Test Method D-1639-70. It is notyet fully understood how non-aqueous substances containing acid affectthe thermochromic, but high acid number substances have inactivated thethermochromic pigments. Generally, the lower the acid number the better.To date ink formulations with an acid value below 20 and not includingthe harmful solvents described above have worked well. Some higher acidvalue formulations may be possible but generally it is best to usevehicle ingredients with low acid numbers or to adjust the acid value byadding an alkali substance. The greatest benefit of a neutral or lowacid value vehicle will be increased shelf life. Buffers have been usedhistorically in offset ink formulations to minimize the effects of thefountain solution on pigment particles. This is one possible solution tothe potential acidity problem of the varnishes. One ingredient oftenused as a buffer is cream of tartar. A dispersion of cream of tartar andlinseed oil can be incorporated into the ink. The net effect is that thepigments in the ink are protected from the acidic fountain solution.

Ink Formulations

The encapsulated thermochromic systems of the present disclosure may bereferred to as pigments. In order to add normal pigment to ink, dye, orlacquer, the pigment itself is ground into the base. This disperses thepigment throughout the base. The addition of more pigment intensifiesthe color. Since the pigment often has a very intense color, it issometimes acceptable for only about 10% of the final ink to be made upof normal pigments.

A base for an ink formulation using encapsulated thermochromic systemsof the present disclosure may be developed using off the shelfingredients. The ink will incorporate, where possible, and be compatiblewith different ink types and solvents with molecular weights larger than100 while avoiding aldehydes, diols, ketones, and, in general, aromaticcompounds. Important considerations with respect to the ingredientswithin the ink vehicle are the reactivity of the ingredients with theencapsulated thermochromic system.

Unwanted interactions between media and the encapsulated thermochromicsystems can occur between compounds found in ink formulations. The longalkyl chains of many of the compounds found in ink vehicles may havereactive portions that can fit through the pores of the capsule andinteract with the inner phase and denature it through this interaction.Since the behavior of the thermochromic system is related to the shapeand the location of its molecules at given temperatures, disruptingthese structures could have a large impact on the characteristics of thethermochromic system. Even molecules that cannot fit through the capsulepores may have reactive portions that could protrude into the capsuleand thereby influence the color transition of the thermochromic systemwithin the capsule. Therefore, mineral spirits, ketones, diols, andaldehydes are preferably minimized in any medium in which theencapsulated are also preferably avoided. If these compounds aresubstantially reduced or eliminated the thermochromic systems willperform better and have a longer shelf life.

Another important step in using the encapsulated thermochromic systemsof the present disclosure in ink formulations is to adjust the pH orlower the acid value of the ink base before the thermochromic system isadded. This can be done by ensuring that each individual component ofthe base is at the correct pH or acid value or by simply adding a protondonor or proton acceptor to the base itself prior to adding thethermochromic system. The appropriate specific pH is generally neutral,or 7.0. The pH will vary between 6.0 and 8.0 depending on the ink typeand the color and batch of the thermochromic system.

Once a slurry and the base have been properly prepared, they arecombined. The method of stirring should be low speed with non-metal stirblades. Other additives may be incorporated to keep the thermochromicsystem suspended. The ink should be stored at room temperature.

Most thermochromic pigments undergo a color change from a specific colorto colorless. Therefore, layers of background colors can be providedunder thermochromic layers that will only be seen when the thermochromicpigment changes to colorless. If an undercoat of yellow is applied tothe substrate and then a layer containing blue thermochromic pigment isapplied the color will appear to change from green to yellow, when whatis really happening is that the blue is changing to colorless.

The substrates that the thermochromic inks are printed upon arepreferably neutral in pH, and should not impart any chemicals to thecapsule that will have a deleterious effect on it.

Thermochromic inks or coatings contain, in combination, a vehicle and apigment including thermochromic microcapsules. The thermochromicmicrocapsules are preferably present in an amount ranging from 1% to 50%of the ink by weight on a sliding scale relative to other pigments. Thevehicle contains a solvent that is preferably present in an amountranging from 25% to 75% by weight of the coating.

The aqueous pigment slurries have particle sizes less than 5 microns andwhen drawn-down on ink test paper and dried, the pigment coating showsreversible thermochromic properties when cooled to the solidificationpoint of the fatty ester, alcohol, amide, or a blend designed to obtaina specific temperature for full color formation. Such pigments can bedesigned to have a range of temperature for transition from fullabsorption temperature (full absorption color or UVA absorption point)to no color or no UVA absorption temperature (clearing point) of 2-7° C.The pigments are very useful for manufacture of ink, coating, andinjected molded plastic products by spray drying prior to formulationinto inks or coating compositions or extrusion into thermoplasticpolymers to produce pellet concentrates for manufacture of injectionmolded thermochromic plastic products such as cups, cup lids, jars,straws, stirrers, container sleeves, shrink wrap labels. For example,thermochromic compositions were identified that permit generation ofhigh quality saturated photographic quality yellow color that is veryuseful to formulate new orange, red, and green colors by mixing withmagenta and/or cyan thermochromic pigments or by initialco-encapsulation of the yellow leuco dye with magenta and/or cyan leucodyes and appropriate color developers during the pigment manufacture.Alternatively leuco pigments were identified that can change fromabsorption mainly in the region from 280 to 350 nm to absorption mainlyfrom 350 to 400 nm. In an embodiment, this leuco dye can be used in aphotochromic gel ink pen as disclosed above.

Ball-Point Pens

Ball-point pens employing the thermochromic inks disclosed herein may beused in a conventional ball-point pen mechanism or marker.

The thermochromic inks disclosed herein are endowed with thixotropicproperties. The thermochromic inks disclosed herein have a highviscosity when left to stand without application of shear stress and isstably held in the ball-point pen mechanism, and only the ink around theball becomes low viscous at the time of writing because of the highshear force attributable to the ball that rotates at a high speed, sothat the ink smoothly passes through a gap between the ball and a ballholder by capillary action and is transferred to the paper surface. Theink transferred to the paper surface or the like is released from shearforce and hence again brought into a highly viscous state, not causingthe feathering in writing.

The thermochromic ink compositions disclosed herein satisfies propertiessuited for ball-point pen inks, can be free from line splitting, blursand blobbing in writing, has stable viscosity characteristics with time,and satisfies practical performances as water-based ball-point pen inkscontaining various colorants. As the colorants, pigments and dyes ofvarious types can be used, and hence ball-point pens having a variety incolor tones can be provided. Also, in the system where the thermochromicmicrocapsular pigment material is used as the colorant, convenientball-point pens that can give thermochromic written images can beprovided, promising the spread of new uses. Such applicable uses andadvantages attributable thereto will be exemplified below.

In an embodiment, confidential images such as letters and pictures thatcause metachromatism at temperature lower than the room temperature canbe formed on post cards, Christmas cards, greeting cards and so forth.Thus, the images may be made to come into sight when cooled, so as to beapplicable to magical use, or images that can alternately change fromcolor (A) to color (B) may be formed so that the metachromatism may becaused by body temperature, hand temperature, or other heat source.

In another embodiment, thermochromic inks disclosed herein are capableof forming color only when it is cold, e.g., at a metachromatictemperature of 10° C., or a thermochromic pigment material havinghysteresis characteristics in a wide temperature range, images thatcannot be read at room temperature can be recorded, using the ball-pointpen of the present disclosure as a confidential pen. Thus, the pen canbe used to write memos or the like that must be made confidential.

In another embodiment, pens using the thermochromic inks disclosedherein can be used for learning in school or the like, e.g., forquestions, tests, drills, blank maps and English translations, wherenecessary answers or remarks are written and the written information iserased by heating so that again the problems or the like can be engagedin the state completely reset to have neither answers nor memos.

In another embodiment, pens using the thermochromic inks disclosedherein can be used for temperature indication as if it functions as athermometer. A set of thermochromic ink ball-point pens having differentmetachromatic temperature may be provided so that various images areformed to make them function as temperature detectors. Thus, the inkcomposition of the present invention can be used in not only toys andstationery but also in a variety of industrial fields, e.g., can beconveniently used in temperature control of reaction tanks, temperaturecontrol of processing steps, indication for suitable temperature controlof low-temperature circulation food, display for preventing overheat dueto short of electric code outlets.

In another embodiment, the thermochromic inks disclosed herein can beused in articles of clothing, illustrations or pictures may be drawn oncasual wear such as T-shirts with a 30° C.-metachromatic thermochromicink ball-point pen so that users themselves can design T-shirts capableof causing metachromatism utilizing a temperature difference between theoutdoors and the room in the summer season. This can also be applied togloves, shoes, hats or caps, ski wear and swimming suits.

In another embodiment, pens using the thermochromic inks disclosedherein can be used for preventing forgery, genuine things and imitationscan be discriminated by cooling or heating. For example, someinformation may be handwritten with the ball-point pen of the presentdisclosure in tickets, merchandize bonds, coupon tickets and so forth ona scale of private concerns or small lots. This can effectively preventforgery.

In another embodiment, pens using the thermochromic inks disclosedherein can be used in combination with usual non-metachromatic inkball-point pens so that the state of changes can be in more variety.

The present disclosure provides thermochromic inks for use in ashear-thinning ball-point pen. In an embodiment, the thermochromic inkcompositions have a viscosity within the range of from about 25 mPas toabout 160 mPas and a shear thinning index adjusted within the range offrom about 0.1 to about 0.6.

The non-limiting embodiments that follow teach by way of example andshould not be construed as unduly limiting the scope of this disclosure.

In one aspect, a reversible thermochromic ink for use in pens contains areversible thermochromic pigment in an amount from 1% to 40% by weightof the coating, and a vehicle forming the balance of the coating. Thevehicle including a resin selected from the group consisting ofpolyester, urethane, acrylic acid and acrylate resins, and combinationsthereof.

Commercially available thermochromic pigments may be readily obtained ina variety of colors demonstrating color transition temperatures fromabout 5° C. and up to about 65° C. A range of color formulations may bemade by mixing the pigment to include one or more of the followingreversible thermochromic colors: yellow, magenta, cyan, and black. Thesemay be further mixed to include other dyes or solid pigments that arenon-thermochromic in nature. The pigment may change from a colorlessstate to a colored state upon cooling to the reactive temperature, or toa colored state upon heating to the reactive temperature. It ispreferred that the microcapsules are formed of urea formaldehyde ormelamine formaldehyde that is acid catalyzed to enhance the inherentstability in polar, low molecular weight solvents having a molecularweight of about less than 100 g/mol.

Thermochromic Inks Used in Pens

In an embodiment, thermochromic inks of the present disclosure containmicroencapsulated leuco dye, developer, and solvent with the appropriatesolvency and melting point to achieve the temperature activated colorchange. In an embodiment, the base colorant is a permanently coloredpigment or dye that is suspended in the ink formulation, or soluble inthe ink formulation.

In an embodiment, the shear thinning ink may be formulated using a filmforming compound such as ethylene maleic anhydride or an equivalentsubstitute fully hydrolyzed in water and adjusted to the desiredthixotropic behavior with xanthan gum. The film forming properties ofthe ink could be achieved using many resins/vehicles such as ethylenemaleic anhydride, styrene acrylonitrile polymers, acrylic emulsions, orurethane emulsions for example. The rheology to achieve the viscosityand shear thinning ability could be controlled by surfactants and agentssuch as xanthan gum and hydroxyl ethyl cellulose as well as a number ofothers.

In an embodiment, the temperature between full color development andclearing point activation can be engineered with a mixture of alkylesters such as methyl palmitate, methyl stearate, isopropyl palmitate,stearyl behenate, and behenyl alcohol to produce the following color tocolor effects, for example: a full color development between 23° C. and27° C. and color clearing between 27° C. and 33° C. for easily activatedreversible thermochromic color to color options.

In an embodiment, ball-point pen and gel-ink pens disclosed herein usethermochromic inks that transition from one color to another color, orfrom color to colorless, when activated at about body temperature or atabout room temperature.

Strong color to color transition and color to colorless examples are asfollows:

Purple to pink Blue thermochromic + pink/red base color Green to yellowBlue thermochromic + yellow base color Orange to yellow Redthermochromic + yellow base color Burgundy to blue Red thermochromic +blue base color Brown to green Red thermochromic + green base colorGreen to blue Yellow thermochromic + blue base color Orange to pinkYellow thermochromic + pink/red base color Blue to colorless Bluethermochromic + white/clear base color Black to colorless Blackthermochromic + white/clear base color

The above embodiments of color to color options are achieved by mixingdifferent ratios of thermochromic microcapsules with standard coloredbases, as described herein. The base colorants may be pigments or dyesthat are compatible in the ink formulation.

The color to color transitions sometimes lack high contrast between thecolor developed state and the base color. In order to increase contrast,black to color transition inks are herein disclosed.

In an embodiment, black to color transitions use blue/cyan, red/magenta,yellow, and black thermochromics with red/magenta, blue/cyan, yellow,and white base colorants. Examples of thermochromic inks having black tocolor transition are as follows:

Black to blue Thermochromic magenta, blue base black, yellow + Black toyellow Thermochromic magenta, yellow base black, blue + Black tored/pink Thermochromic blue, pink/magenta base yellow, black + Black toorange Thermochromic blue, pink and yellow base black + Black to greenThermochromic magenta, blue and yellow base black + Black to violetThermochromic yellow, blue and pink base black + Black to brownThermochromic blue, pink, yellow, blue base black +

By mixing different ratios of thermochromic pigments with standardcolored bases, a neutral black to almost any colored base is possible.These black to color transitions can be used to create black and whiteimages that will change to colored states when heat activated.

Photochromic Ink Pens

In an embodiment, photochromic microcapsules can also be formulated byencapsulating photochromic dyes in resins, monomers, and polymers usingstandard encapsulating techniques to achieve a particle size between 300nm and 5 microns. For example, in situ or interfacial polymerizationusing melamine resin, epoxy resin, or urea-formaldehyde may be used toencapsulate hydrophobic, water immiscible internal phase materials inwhich the dye is dissolved. Antioxidants, hindered amine lightstabilizers, and UV absorbers may be used either alone or in combinationwith each other to enhance the UV stability of the system. The internalphase solvent may be maintained as a liquid, or polymerized to a solidwithin the microcapsule.

The microencapsulated photochromic systems then can be formulated into awater-based shear thinning gel ink for use in roller ball pens. Inks canbe produced that are virtually invisible under normal fluorescent orincandescent lighting indoors, but which will develop vibrant colorsunder UV light such as natural sunlight. By mixing colored bases withthe photochromic inks, color to color development is also possible. Theshear thinning properties and film forming properties of the ink can beachieved using many resins/vehicles such as ethylene maleic anhydride,styrene acrylonitrile polymers, acrylic emulsions, or urethane emulsionsfor example.

The rheological manipulations to achieve the viscosity and shearthinning of the photochromic inks can be controlled by surfactants andagents such as xanthan gum, hydroxyl ethyl cellulose and various otheragents well known in the art. The end result is a gel ink that flowsfrom a roller ball pen smoothly so as to form a uniform ink line withoutstarving or blobbing.

Embodiments of photochromic inks useful in pens include:

Colorless to Blue Microencapsulated blue + Clear gel base Yellow toGreen Microencapsulated blue + Yellow base color + Clear gel baseColorless to Red Microencapsulated red + Clear gel base Blue to PurpleMicroencapsulated red + Blue base color + Clear gel base

Examples Black to Green Temperature Memory Ink

A thermochromic ink composition, commercially available from ChromaticTechnologies Inc., with full color between 12° C. and 15° C. and colorclearing between 21° C. and 27° C. for a color to color option was madeso that the color of the thermochromic portion of the ink was maintainedup to room temperature, but easily activated by body temperature to aclearing point to reveal the base color.

The thermochromic ink was a composition consisting of a thermochromicblue dye with a magenta leuco dye, and a developer to achieve areversible thermochromic system with a full color development around 12°C. and a clearing temperature of 25° C. Magenta thermochromic capsuleswere incorporated into a water-based shear thinning gel ink with a neonblue pigmented gel ink and a neon yellow pigmented gel ink.

The shear thinning thermochromic ink was formulated using a film formingcompound such as ethylene maleic anhydride fully hydrolyzed in water andadjusted to the desired thixotropic behavior with xanthan gum.

The result was an aqueous ink that appeared black when cooled to atemperature below 12° C. and remained black until heated to atemperature above 25° C. when it changed to a bright green color.

The thermochromic reversible color changing ink was injected into astandard 0.7 mm to 1.0 mm tip gel ink pen for transfer to a papersubstrate.

In an embodiment, a drawing or written image could then be made thatwill appear black at room temperature. In an embodiment, the coloredimage may easily be activated to the bright orange by gentle rubbing andthe black color can only be regained by cooling to a temperature around12° C. for a few minutes.

The color to color options are achieved by mixing different ratios ofthermochromic microcapsules with standard colored bases. The basecolorants may be pigments or dyes that are compatible in the inkformulation. These color to color options are artistically pleasing, butare somewhat limited as far as high contrast between the color developedstate and the base color. Thermochromic pigments are commerciallyavailable from Chromatic Technologies Inc. in Colorado Springs, Colo.

In order to achieve a maximum color effect for artistic reasons, neutralcharcoal/black to color options are proposed. In one example that showsthe mixing of colors, these thermochromic pigments:

-   -   blue/cyan, red/magenta, yellow, and black may be mixed with the        following base colorants (pigments or dyes):        -   red/magenta, blue/cyan, yellow, and white.        -   Moreover, any neutral black to color option is achievable.

This is achieved by mixing different ratios of thermochromic pigmentswith standard colored bases. It is possible to achieve a neutral blackto almost any colored base is possible. This allows full dramatic effectto such an extent that the user can create a black and white image thatwill change to the colored state when heat activated. For example,picture a natural setting of a tree on a hillside. The trunk of the treewill be black to brown, the leaves of the tree will be black to green,the sun will be black to orange and black to yellow, the grass on thehillside will be black to green, and clouds will be black to blue. Byselectively choosing the black to color option, any scene can bedepicted that will transition from the neutral black sketch to a fullycolored sketch as it is heated.

The thermochromic component of the invention is a microencapsulatedleuco dye, developer, and solvent with the appropriate solvency andmelting point to achieve the temperature activated color change.

The base colorant is a permanently colored pigment or dye that issuspended in the ink formulation, or soluble in the ink formulation.

The temperature between full color development and clearing pointactivation can easily be engineered with a variety of internal phasesolvents as described in a number of patents to achievemicroencapsulated pigments with color development between −10 C and 65C.

Example of Black to Orange

A microencapsulated pigment with an internal phase engineered with ablue leuco dye and a phenolic developer to achieve a reversiblethermochromic system with a full color development between 23 C and 27 Cand a clearing temperature between 28 C and 31 C (available fromChromatic Technologies, Inc.)

The red thermochromic capsules are incorporated into a water-based shearthinning gel ink with a neon pink pigmented gel ink and a neon yellowpigmented gel ink.

The shear thinning ink may be formulated using a film forming compoundsuch as ethylene maleic anhydride fully hydrolyzed in water and adjustedto the desired thixotropic behavior with xanthan gum. The film formingproperties of the ink could be achieved using many resins/vehicles suchas ethylene maleic anhydride, styrene acrylonitrile polymers, acrylicemulsions, or urethane emulsions for example. The rheology to achievethe viscosity and shear thinning ability could be controlled bysurfactants and agents such as xanthan gum and hydroxyl ethyl celluloseas well as a number of others.

A thermochromic ink composition, commercially available from ChromaticTechnologies Inc., consisting of a thermochromic blue with a blue leucodye and a developer to achieve a reversible thermochromic system with afull color development around 27° C. and a clearing temperature of 32°C. was produced. The blue thermochromic microcapsules were incorporatedinto a water-based shear thinning gel ink with a neon pink pigmented gelink and a neon yellow pigmented gel ink.

The resulting thermochromic ink appeared black when below 27 C andgradually changed to a bright orange when heated to a temperature above32 C.

The thermochromic reversible color changing ink was injected into astandard 0.7 mm to 1.0 mm tip gel ink pen for transfer to a papersubstrate.

Black to Orange Color Changing Thermochromic Pen/Marker Formulation

Amount Component (g) wt % Ethylene maleic anhydride solution (10-20%)10-20 6.7-10 Xanthan gum solution (0.25%) 10-20 6.7-10 Blue microcapsuleslurry (40-50% capsule solids) 30-40 26.7-30  Black microcapsule slurry(40-50% capsule solids) 10-20 6.7-10 Pigmented yellow gel ink (20-30%pigment solids) 20-25 16.7-20  Pigmented pink gel ink (20-30% pigmentsolids) 20-25 16.7-20  Water-based anti-foaming surfactant 0.5-1.00.25-0.5 

The result is an ink that will appear black when below 27° C. andgradually change to a bright orange when heated to a temperature above31° C.

The thermochromic reversible color changing ink is injected into astandard 0.7 mm to 1.0 mm tip gel ink pen for transfer to a papersubstrate. As non-limiting examples the ink formulated can be for a ballpoint pen or a fibrous tip marker type writing instrument.

A nonlimiting example of a Purple to pink Temperature Memory Ink:

Full color between 12° C. and 15° C. and color clearing between 21° C.and 27° C. for a color to color option so that the color of thethermochromic portion of the ink is maintained up to room temperature,but easily activated by body temperature to a clearing point to revealthe base color. A microencapsulated pigment engineered to have a widehysteresis effect using a magenta dye and a phenolic developer toachieve a reversible thermochromic system with a full color developmentbetween 12-13° C. and a clearing temperature between 23-25° C.

The blue thermochromic capsules are incorporated into a water-basedshear thinning gel ink with a neon pink pigmented gel ink.

The shear thinning ink is formulated using a film forming compound suchas ethylene maleic anhydride fully hydrolyzed in water and adjusted tothe desired thixotropic behavior with xanthan gum.

The result is an aqueous ink that will appear purple when cooled to atemperature below 12 C and will remain purple until heated to atemperature above 23-25° C., where it will then change to a bright pinkcolor.

The thermochromic reversible color changing ink is injected into astandard 0.7 mm to 1.0 mm (or larger) tip gel ink pen for transfer to apaper substrate.

A drawing or written image can be made that will appear purple at roomtemperature (20-23 C). The colored image may easily be activated to thebright pink by gentle rubbing or heating. The purple color can only beregained by cooling to a temperature around 12° C. for a few secondsachievable by placing the printed image in a refrigerator set at normalconditions.

Photochromic Gel Ink Pen

Photochromic microcapsules can also be formulated by encapsulatingphotochromic dyes in resins, monomers, and polymers using standardencapsulating techniques to achieve microcapsules suitable for use as apigment in a gel ink. For example, in situ or interfacial polymerizationusing melamine resin, epoxy resin, or urea-formaldehyde may be used toencapsulate hydrophobic, water immiscible internal phase materials inwhich the dye is dissolved. Antioxidants, hindered amine lightstabilizers, and UV absorbers may be used either alone or in combinationwith each other to enhance the UV stability of the system. The internalphase solvent may be maintained as a liquid, or polymerized to a solidwithin the microcapsule. The microencapsulated photochromic systems thencan be formulated into a water-based shear thinning gel ink for use inroller ball pens. Inks can be produced that are virtually invisibleunder normal fluorescent or incandescent lighting indoors, but whichwill develop vibrant colors under UV light such as natural sunlight. Bymixing colored bases with the photochromic inks, color to colordevelopment is also possible. The shear thinning properties and filmforming properties of the ink could be achieved using manyresins/vehicles such as ethylene maleic anhydride, styrene acrylonitrilepolymers, acrylic emulsions, or urethane emulsions for example. Therheology to achieve the viscosity and shear thinning ability could becontrolled by surfactants and agents such as xanthan gum and hydroxylethyl cellulose and a number of others. The end result would be a gelink that would flow from a roller ball pen smoothly so as to form auniform ink line without starving or blobbing.

Clear Base Gel

The nonlimiting example that follows shows one embodiment for a clearbase gel incorporating the instrumentalities described above. The cleargel base can be formulated as follows:

Amount Component (g) wt % Ethylene maleic anhydride solution (10-20%)40-50 40-50 Xanthan gum solution (0.25%) 40-50 40-50 Anti-foamingsurfactant 0.25-0.50 0.25-0.50

This may be mixed with pigment as follows. The amount of the pigment isadded to suit the eye.

Colorless to Blue: Microencapsulated blue + Clear gel base Yellow toGreen: Microencapsulated blue + Yellow base color + Clear gel baseColorless to Red: Microencapsulated red + Clear gel base Blue to Purple:Microencapsulated red + Blue base color + Clear gel base

In general 50-98% gel base is blended with 1-50% photochromic dye ormicroencapsulate photochromic dye, and 1-50% of a colored dye.Preferably, 60-95% mixed with 5-40% photochromic dye ormicroencapsulated dye, and 1-10% of a colored dye.

An example photochromic yellow to green pen/marker ink is:

-   -   90% gel base    -   5% photochromic microencapsulated pigment    -   5% Tartrazine dye

Additional temperature profiles with various degrees of color memory maybe achieved with other internal phase materials such as tetradecanol,dodecyl decanoate, and decanophenone, where the color may be fullydeveloped at a lower temperatures and maintained until some higherclearing point temperature.

The foregoing disclosure teaches by way of example, and not bylimitation. Those skilled in the art will appreciate that what isclaimed may be subjected to9insubstatial change with9ut departing formthe scope and spirit of the invention. Accordingly. the inventors herebystate their intention to rely upon the doctrine of Equivalents, in orderto protect their rights in the invention.

1-16. (canceled)
 17. A thermochromic ink for a writing instrument, saidthermochromic ink comprising: a reversible thermochromic pigmentsusceptible to a temperature-modulated color change associated withreversible thermochromic pigment first and second states along ahysteresis loop; a non-thermochromic colorant; and a vehicle; whereinsaid reversible thermochromic pigment and said non-thermochromiccolorant provide said thermochromic ink with a thermochromic ink firstcolor when said reversible thermochromic pigment is in said reversiblethermochromic pigment first state and wherein said reversiblethermochromic pigment and said non-thermochromic colorant provide saidthermochromic ink with a thermochromic ink second color when saidreversible thermochromic pigment is in said reversible thermochromicpigment second state.
 18. The thermochromic ink of claim 17, whereinsaid reversible thermochromic pigment and said non-thermochromiccolorant are present in a ratio in a range of 1:1 to 1:3 by weight. 19.The thermochromic ink of claim 17, wherein said reversible thermochromicpigment has a hysteresis window of less than about 5 degrees centigrade.20. The thermochromic ink of claim 17, wherein said reversiblethermochromic pigment has a hysteresis window of greater than about 60degrees centigrade.
 21. The thermochromic ink of claim 17, wherein saidreversible thermochromic pigment has a hysteresis window of greater thanabout 80 degrees centigrade.
 22. The thermochromic ink of claim 17,wherein said vehicle is formulated to have a pH in a range of betweenabout 6.0 to about 8.0.
 23. The thermochromic ink of claim 17, whereinsaid reversible thermochromic pigment comprises substantially sphericalmicrocapsules having a diameter of less than about 5 micrometers. 24.The thermochromic ink of claim 17, wherein said reversible thermochromicpigment comprises substantially spherical microcapsules having adiameter of less than about 3 micrometers.
 25. The thermochromic ink ofclaim 17, wherein said non-thermochromic colorant is selected from thegroup consisting of: a pigment, a dye, and a photochromic dye.
 26. Thethermochromic ink of claim 17, wherein said non-thermochromic colorantis a microencapsulated photochromic dye.
 27. The thermochromic ink ofclaim 17, further comprising one or more additional thermochromicpigments.
 28. The thermochromic ink of claim 17, wherein said reversiblethermochromic pigment first state is a colored state and said reversiblethermochromic pigment second state is substantially colorless.
 29. Thethermochromic ink of claim 17, wherein said thermochromic ink isformulated to change from black to a color other than black uponheating.
 30. The thermochromic ink of claim 17, wherein saidtemperature-modulated color change is triggered by about bodytemperature.
 31. The thermochromic ink of claim 17, wherein saidtemperature-modulated color change is triggered by human touch.
 32. Thethermochromic ink of claim 17, wherein said thermochromic ink has aviscosity in a range of between about of 25 mPas to about 160 mPas. 33.The thermochromic ink of claim 17, wherein said thermochromic ink has ashear-thinning index in a range of between about 0.1 to about 0.6. 34.The thermochromic ink of claim 17, wherein said thermochromic ink isformulated as a gel ink.
 35. The thermochromic ink of claim 17, whereinsaid thermochromic ink is formulated as a water-based shear-thinning gelink.
 36. The thermochromic ink of claim 17, wherein said writinginstrument is selected from the group consisting of: a gel-ink pen, aball-point pen, a roller-ball pen, and a marker.